1. Field of the Invention
The present invention relates to a winder for winding a traveling web, such as a paper web, into a roll.
2. Description of the Related Art
In the winding of webs, the winding hardness, or tightness, plays a major role in view of subsequent processing. Especially with paper webs it is quite decisive for the winding tightness to have a certain progression over the entire paper roll diameter. The winding tightness should generally decline from a certain starting value to an ending value. The decline should be maximally uniform from the first to the last ply. It should have a certain gradient, that is, should not be too heavy and not too little. Most of all, the winding tightness should not involve any jump, for instance a sudden drop.
This is accomplished only through specific measures. When doing nothing, the line pressure between the paper roll and the drum(s) becomes ever greater with increasing paper roll diameter, and thus also the winding tightness.
To avoid this, e.g., so-called rider rolls are used, which are arranged axially parallel to the drums and serve to exert a nip on the paper roll. The nip is controlled to be high at the start and diminishes with increasing paper roll weight. Thus, the rider roll allows influencing the line pressure and with it also the winding tightness, controlling it in the desired sense. When forming a paper roll with a very large diameter is desired, also the line pressure is very high in the end phase of winding. The winding tension increases as well, giving rise to web burst or crepe wrinkles.
Other measures to influence the winding tightness consist in distributing the load of the paper roll to the individual drums. For that purpose, drums of equal diameter were arranged already at different horizontal planes, or drums of different diameters were used. Moreover, it is known that winding with a drum of smaller diameter produces a tighter winding than is obtained with a drum of larger diameter.
DE-U1-91 15 481 shows and describes a winder for web-to-roll winding with a relieving device for application of compressed air on the shell surface of the paper roll. Employed is a blowing space formed of the two bed rolls of the winder, a partitioning wall that bridges the clearance between the shell surfaces of the two drums, of two end walls and of the shell surface of the paper roll itself.
EP 0 631 954 A2 shows and describes a bed roll winder with two drums. It employs a pressure-tight space that encloses the entire paper roll and has walls which approach in the bed roll area their shell surfaces and are sealed at that point. Application of a vacuum at the sealed space, or partial spaces, allows exerting a corresponding force on the paper roll, thereby relieving it more or less of its deadweight, so that thereafter a floating of the paper roll on the drums may come about.